Process for preparing graft copolymers containing n,n-di(beta-hydroxyethyl) glycine salts

ABSTRACT

A COMPOSITION COMPRISING A GRAFT COPOLYMER RESIN AND THE ALKALI METAL SALT OF N, N-DI(BETA-HDROXYETHYL) GLYCINE IS CHARACTERIZED BY IMPROVED COLOR AND GLOSS CHARACTERISTICS.

United States Patent 3,662,026 PROCESS FOR PREPARING GRAFT COPOLYMERSCONTAINING N,N-DI(BETA-HYDROXYETHYL) GLYCINE SALTS George L. Rushton,Trenton, N.J., assignor to Cities Service Company, New York, N. NoDrawing. Filed June 1, 1970, Ser. No. 42,574 Int. Cl. C08f /04 U.S. Cl.260-880 R 7 Claims ABSTRACT OF THE DISCLOSURE A composition comprising agraft copolymer resin and the alkali metal salt ofN,N-di(beta-hydroxyethyl)glycine is characterized by improved color andgloss characteristics.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the improvement of the color and surface gloss of polymericcompositions. More specifically, it relates to a method for improvingthe color and gloss of a graft copolymer formed by the polymerization ofan unsaturated monomer or mixture of unsaturated monomers in thepresence of a polymeric substrate. In another aspect it relates to agraft copolymer composition containing an alkali metal salt ofN,N-di(beta-hydroxyethyl) glycine incorporated therein.

The polymerization of various monomers or monomer mixtures in thepresence of a polymeric substrate is known. For example, thepolymerization of a vinyl aromatic monomer, exemplified by styrene, anda vinyl cyanide monomer, exemplified by acrylonitrile, or mixturesthereof, in the presence of an aqueous emulsion of an ethylenicallyunsaturated substrate, such as a butadiene polymer latex orbutadiene-styrene copolymer latex, is well known. Such polymerizationreactions, which often are initiated by a free radical source and employsufiicient water and surfactant to emulsify the monomers, result in atleast partial grafting of the monomers onto the polymeric substrate toproduce synthetic resins having superior physical and chemicalproperties. A wide variety of such synthetic resins, as well as suitablesynthesis procedures, polymeric latices, monomer mixtures andproportions of reactants is described in the literature. These resinscan also be prepared by methods such as graft suspension polymerization,mass polymerization, and resin blending. One of the better known resinsis prepared by graft polymerizing a mixture of vinyl aromatic and vinylcyanide monomers onto a polymeric substrate.

The physical properties of resins produced by these myriad proceduresare primarily dependent on the proportions of the polymeric substrateand monomer employed in the polymerization, the specific reactionconditions, the type of free radical initiators and the type ofmolecular Weight regulators. High impact strength is one of theimportant physical characteristics of such resins.

Recent developments have concentrated on procedures for improving thesurface gloss and color of resins of this type. Such resins, as producedby the above indicated methods, can be prepared in the form of powders,beads or flakes and they are often processed and'shipped in the form ofpellets. Desirably, these base resins are as colorless as possibleinsofar as any discoloration will, of course, cause problems in thecolor of the finished product; variations in the base resin color willresult in variations of the product as later pigmented. Such variationswill require a subsequent processor to engage in extensive colormatching, resulting in production interruptions and increased 3,662,026Patented May 9, 1972 cost. The aforementioned discoloration can arisefrom a manufacturing step, such as may be caused by a contaminatedreactor, or it can be the result of a processing step, such as extrusionat too high a temperature. Manufacturing methods that minimizediscoloration are desirable. From the foregoing comments, it is apparentthat a means for reducing or inhibiting the formation of color bodiesduring either the manufacture or processing of resins would be ofsignificant benefit.

Another important and desirable property of graft copolymer resins issurface gloss. A dull, or controlled gloss, or matte finish is desirablefor some products such as luggage. With other products, however, such astelephone hand sets and appliance housings, a shiny glossy finish ispreferred. Surface gloss is affected by, among others, latex properties,the method of grafting the monomers onto the polymeric substrate,molding pressure and the presence of various additives. Each of thesefactors, however, may affect other properties of the resin such asimpact strength and/or tensile strength. A base resin that can beprocessed to a product having a minimum of discoloration and a maximumof surface gloss without the addition of deleterious materials isdesirable. This invention provides such a resin.

SUMMARY OF THE INVENTION It has now been found that when the alkalimetal salt of N,N-di(beta-hydroxyethyl) glycine is incorporated in agraft copolymer resin a composition is obtained which is characterizedby improved color and surface gloss properties.

In one embodiment of this invention, the alkali metal salt ofN,N-di(beta-hydroxyethyl)glycine can be added to the mixture of polymerlatex and monomers, prior to polymerization. In another embodiment ofthis invention the alkali metal salt of N,N-di(beta-hydroxyethyl)glycinecan be added to the reaction mixture subsequent to polymerization butprior to coagulation, as will be discussed more fully below.

In general, the preparation of the graft copolymer resins isaccomplished by the polymerization of an unsaturated monomer or mixturethereof in the presence of a polymeric substrate. A preferred methodinvolves graft emulsion polymerization methods in which suitablemonomers are polymerized in a polymeric emulsion latex under graftingconditions. Other methods, such as graft suspension polymerization andthe physical blending of copolymer resins, can be used to preparepolymer resins amenable to treatment as disclosed herein.

In accordance with the present invention the polymeric substrate, in thecase of emulsion polymerization technique, is a polymer latex whoseconstituting unit can be a single diolefin series, for example a naturalrubber latex, polyisoprene latex, polybutadiene latex or.p'olychloroprene latex. Additionally, the polymeric substrate can beobtained by copolymerizing at least one mono-olefin with a conjugateddiolefinic hydrocarbon, for example butadieneisobutylene copolymerlatex; butadiene-styrene copolymer latex; butadiene-acrylonitrilecopolymer latex; butadienemethyl methacrylate copolymer latex;butadiene-styreneacrylonitrile terpolymer latex; andbutadiene-styrene-vinyl pyridine terpolymer latex. Polybutadiene andpoly (butadiene-styrene) are preferred. The unsaturated monomer ormixtures therof can be selected from among the vinyl aromatic monomers,vinyl cyanides, acrylates, methacrylates, vinyl halides, hydrocarbons,vinyl esters, vinyl ethers, vinyl "pyridine, alkylesters of unsaturatedacids, vinyl ketones, allyl chlorides and allyl acetates. In a preferredembodiment the monomers are selected from vinyl aromatic monomers, vinylcyanide monomers and mixtures thereof.

The vinyl aromatic monomers are desirably selected from those compoundsof the benzene series having the vinyl radical directly attached to acarbon atom of the aromatic nucleus, such as styrene, alpha-methylstyrene, vinyl toluene, vinyl xylene, isopropyl styrene, ethyl vinylbenzene, and halogenated derivatives thereof. In a preferred embodimentthe vinyl aromatic monomer is selected from styrene and alpha-methylstyrene, with styrene being especially preferred.

The vinyl cyanide monomer is desirably selected from acrylonitrile andmethacrylonitrile and can be partially replaced, if desired, withvarious esters and derivatives of the acrylic acid series. It ispreferred to use acrylonitrile.

The polymeric substrate and unsaturated monomers can be combined in avariety of proportions, resulting in a graft copolymer resin which cancontain, in one embodiment, from about to about 35% by weight of thepolymeric substrate, from to about by weight of the vinyl cyanidemonomer and from about to about 80% by weight of vinyl aromatic monomer.

As indicated above, in producing the polymer composition of the presentinvention the polymerization may be carried out by ordinary emulsionpolymerization. Thus, the polymerization may be carried out by using afatty acid soap, alkyl sulfonate, alkyl sulfate, disproportionatedrosinate or nonionic surface active agent as an emulsifier, and a freeradical catalyst such as azobisisobutyronitrile or a redox catalyst suchas a persulfate or peroxide as a polymerization initiator at atemperature above about 20 C. but below about 95 C.

In such case, the molecular weight in the polymerization can beregulated by the addition of a polymerization regulator such asn-dodecyl and mixed tertiary mercaptans, for example those containing amixture of C C and C mercaptans. Further, before the start or after thecompletion of the polymerization, as antioxidant such asbeta-naphthylamine or a butylated bisphenol-A can be added.

The polymerization reaction is typically continued until the reaction issubstantially completed. At the end of the reaction the reaction productis coagulated, for example, with a solution of calcium chloride, washedand then dried by any suitable means.

Resins prepared as indicated above have improved gloss and color whenthe alkali metal salt of N,N-di(beta-hydroxyethyl)glycine isincorporated therein. The salts which are useful within the scope of thepresent invention are available from a variety of sources. In one aspectthe salts are available by neutralizing N,N-di(beta-hydroxyethyl)glycine with an appropriate alkali metal compounds, such as an alkalimetal hydroxide. It should be noted at this point that N,N di(betahydroxyethyl)glycine is an article of commerce, and it therefore isreadily available. In another more direct fashion, the desired salts,such as the sodium salt, are commercially available from, among others,Geigy Industrial Chemicals and Hampshire Chemical Div. of W. R. Graceand Company. While the alkali metal derivatives ofN,N-di(betahydroxyethyl)glycine are generally useful, it is preferred touse either the potassium or sodium derivatives, with the sodiumderivative being especially preferred.

The alkali metal salt of N,N-di(beta-hydroxyethyl) glycine can beincorporated into the graft copolymer resins in a variety of ways. Bestresults are obtained when the salt is added to the completed resinsubsequent to polymerization but prior to coagulation. The salts can beadded in any convenient form and, where an emulsion polymerizationsystem is used, the salt is most simply incorporated as an aqueoussolution. The compositions of this invention contain an amount of thealkali metal salt of N,N- di(beta-hydroxyethyl) glycine sufiicient toimprove the gloss and color. While it is possible that for variousbatchesand various graft copolymer resin systems varying amounts of thesalt might be required, it has been found that, in

general, from about 0.05% to about 0.5% of the salt,

based on the weight of the resin'composition, is usually adequate. It ispreferred to use from about 0.1% to about 0.3% by weight of the graftcopolymer composition. Although these salts can be used in amountsgreater than about 0.5 by weight, the addition of a large excess isundesirable insofar as the system might coagulate.

DESCRIPTION OF THE PREFERRED EMBODIMENT Example I 592 parts by weight ofa butadiene-styrene copolymer latex containing 25% bound styrene andcharacterized by a solids content of about an average particle size of0.5 micron and a gel content of about 77%, 852 parts by weight ofstyrene, 282 parts by weight of acrylonitrile, 7.1 parts by weight ofpotassium persulfate free radical initiator, 7.1 parts by weight ofmixed C C and C mercaptan chain length regulators and 540 parts byweight of demineralized water were combined thusly: The styrene andacrylonitrile monomers, plus the chain length regulator, were combinedand mixed thoroughly. The latex, diluted with approximately 50% of thedemineralized water, was added to a reactor, followed by the addition ofone-half the monomer-chain length regulator mixture. This mixture wasgradually heated to the reaction temperature of 70 C., at which time thefree radical initiator, dissolved in the remaining 50% of thedemineralized water was added. The temperature was maintained at 70 C.One hour after the addition of the initiator, the remaining half of themonomer-chain length regulator mixture was added gradually over a periodof two hours, while maintaining the reaction temperature at 70 C. Thereaction was continued for an additional hour, resulting in a total offive hours at 70 C. About 15 minutes prior to the end of the reactionperiod, 15 parts by weight of ditert. butyl-para-cresol, an antioxidant,was added. The resin was isolated from the polymerization mixture bycoagulation in a 1% solution of calcium chloride, followed by washingand drying. The dried resin powder was used directly in an injectionmolding machine for the preparation of test samples. Color and glosstests were made upon test bars, one inch by six inches by one-eighthinch, injection molded at a temperature of approximately 440 F. Colorwas evaluated as follows: A graft copolymer of acrylonitrile and styreneon a polybutadiene substrate having a brightness of approximately 50 asdetermined according to the CIE tristimulus method was given a value of100 color units. A second acrylonitrile-butadiene-styrene graftcopolymer having a brightness of about 25 (CIE tristimulus) was given avalue of 80 color units. These two resins were combined in 5% increments(95- 5 90-10%, etc.) and molded into test bars so that twenty test barshaving color unit designations between 80 and 100 were obtained. CIEtristimulus coordinates were determined for selected test bars, asreported below. All determinations were run on a Bausch & Lomb-Spectronic 505 Recording Color Spectrophotometer using CIE illuminant C.Results are reported according to the selected-ordinate method.

TABLE I Brightness Color units X Y Z lOOY) stimulus values of the color.A complete discussion of the theory and practice relative to the CIEsystem can be found in Principles of Color Technology by Billmeyer andSaltzman (Interscience, 1966).

The gloss test was made on a test bar having the dimensions of the colorbar, and surface gloss was determined by a Gardner Glossmeter.

In each of the runs set forth in the table below, the additive wasevaluated by preparing the resin as indicated above and by incorporatingthe indicated percentage of the additive in the latex mixture prior topolymerization. In all cases the amount is indicated as weight percentof a completed copolymer composition.

Added at completion of polymerization reaction, but before coagulation.

It can be seen from the foregoing examples, tabulated in Table II, thatthe untreated resin has a gloss of 70 and a color 80, and that thevarious additives failed to substantially alter the gloss or colorcharacteristics of the resin. It is seen that it is only the alkalimetal salt of N,N-di(beta-hydroxyethyl)glycine which provides asubstantial change in both gloss and color. It will also be seen thatthe desirable results are similarly obtained irrespective of whether thealkali metal salt of N,N-di(betahydroxyethyDglycine is added to themixture of mono mers prior to polymerization or whether it is added tothe completed resin subsequent to polymerization but prior tocoagulation. The use of 0.1 wt. percent potassium salt ofN,N-di(beta-hydroxyethyl)glycine provides equivalent results withrespect to gloss and color.

I claim:

1. In a process for emulsion polymerizing about 40- by weight of a vinylaromatic monomer and about 15-35% by Weight of a vinyl cyanide monomerin the presence of about 5-35 by weight of a conjugated diene polymer toform a graft copolymer emulsion and subsequently coagulating thisemulsion to recover the graft copolymer composition, the improvementwhich comprises incorporating into the graft copolymer compositionbefore the coagulation step about ODS-0.5%, based on the weight of thegraft copolymer composition, of an alkali metal salt ofN,N-di(beta-hydroxyethyl) glycine.

2. The process of claim 1 wherein the alkali metal salt is added to theemulsion of monomers and conjugated diene polymer before polymerization.

3. The process of claim 1 wherein the alkali metal salt is added to thegraft copolymer emulsion after completion of the polymerization.

4. The process of claim 3 wherein the amount of alkali metal saltemployed is about 0.l-0.3%.

5. The process of claim 3 wherein the alkali metal salt is the sodiumsalt.

6-. The process of claim 5 wherein the vinyl aromatic monomer is styreneor aplha-methylstyrene, the vinyl cyanide monomer is acrylonitrile ormethacrylonitrile, and the conjugated diene polymer is polybutadiene ora butadiene-styrene copolymer.

7. The process of claim 6 wherein the vinyl aromatic monomer is styreneand the vinyl cyanide monomer is acrylonitrile.

References Cited UNITED STATES PATENTS 3,068,192. 12/1962 White 2608803,341,623 9/1967 Hahn 260-4380 FOREIGN PATENTS 923,843 4/1963 GreatBritain 260--93.5 W

JAMES A. SEID-LECK, Primary Examiner

